The communications revolution of the past few years has seen an explosion in the number of wireless devices. Cellular telephones, personal digital assistants (PDAs), laptops, and other consumer devices are using wireless technology to provide connectivity to their users. Wireless technology is currently being used to provide voice-based services for cellular and PCS (Personal Communication Services) telephones, with increasing need for into building coverage. PDAs and laptops can now access the Internet and local dedicated intranets, giving end users access to not only email but also to World Wide Web based content. The increased demand for access to more services in more locations imposes higher performance demands on the wireless infrastructure.
One major problem facing wireless networks is backhaul data transmission. As cellular and PCS voice utilization inside buildings increases and as the data transfer rate provided to the end user increases, the backhaul network feeding the localized wireless nodes gets heavily burdened. Each local wireless node servicing local wireless end users must be fed traffic from public and/or private, voice and/or data networks. As each end user demands coverage in more areas and higher data throughput, the backhaul network, the network that feeds the localized wireless nodes that actually distribute data traffic to individual end users, has to provide more and more data capacity. Further, as wireless data speed requirements increase, cell sizes—the area serviced by the localized wireless nodes—must shrink. As cell density increases, then, so does the number of backhaul nodes and links that are needed to feed the cells. In fact, the number of backhaul links increases inversely with the square of the wireless nodes' cell radius.
Because of the above, high speed, high capacity wireless networks have generally been limited by backhaul bandwidth. Such bandwidth, previously provided by copper, optical or microwave radio links, comes at a very great cost to the operator and deployer of the wireless network. A wireless backhaul is clearly an attractive alternative.
However, network designers do face difficulties in using wireless technology to link the wireless nodes (which distribute the signals to a wireless end user) back to the wired network. It is desirable to maximize the range between the wireless nodes and the wired network to provide the operator with the greatest freedom in network deployment location. However, many deployments, such as in dense urban areas, do not allow for line of sight links from all wireless nodes to the wired network interface. Even if line of sight is possible, the variable propagation performance of wireless links and the constant changes in the nature and location of traffic demand make dedicated point to point links less than optimal. In addition, hauling all links back to a central point leads to high signal congestion at that point.
Previous attempts to remedy the above issues have met with limited success. A number of patents assigned to Metricom, Inc. have attempted to solve the above issues. U.S. Pat. No. 5,479,400 envisions a multipoint to multipoint system with relay nodes receiving multiple wireless signals from multiple repeater nodes. Unfortunately, the system suffers from the possibility of signal congestion at both the repeater and the relay nodes.
SkyPilot Networks, Inc. (www.skypilot.com) proposes a similar multipoint to multipoint wireless network with every subscriber node being coupled to every other node surrounding it. Data can then travel across any one of the links to arrive at the destination. Unfortunately, the performance of this type of network is highly dependent on the presence and location of the subscriber's equipment. It suffers from limits to scalability—since each subscriber node is potentially a connecting link for all traffic, each subscriber node can potentially become clogged with data traffic. In addition, there are problems in seeding initial network coverage. Furthermore, there is a greater potential lack of privacy between subscribers since each node can become an intercept point for network wide data leaks.
Mesh Networks, Inc. (www.meshnetworks.com) has taken a similar approach with a different application and implementation in mind. An ad hoc wireless peer to peer network is created using low power mobile end user wireless devices. User devices, now mobile, become integral routing points for data traveling through the network. Unfortunately, this approach requires large numbers of end user devices in a given area to work properly. Furthermore, the unpredictable nature of the end users' presence and location, most of whose devices will form part of the routing network, makes for unpredictable and potentially unreliable system availability and performance.
What is therefore required is a system that mitigates the drawbacks of the prior art and provides an improved solution. The solution should ideally allow flexible allocation of higher bit rates between nodes and should be readily deployable in non line of sight environments, offering reliable service to all subscribers at each node.